1. Field of the Invention
The present invention relates to a hydraulic power steering apparatus, and more particularly to a hydraulic power steering apparatus in which a check valve is disposed between a rubber hose provided in a fluid path for feeding operation fluid from a pump and a control valve for supplying the operation fluid to a power cylinder.
2. Description of the Related Art
In a conventional power steering apparatus, in order to reduce pulsation or variations in the pressure of operation fluid discharged from a pump, a rubber hose is disposed in a fluid path for supplying the operation fluid from the pump to a control valve. However, when a vehicle travels on an uneven road surface and a resistance force (so-called kick-back force) is input to a tire to be steered, the rubber hose expands and allows the operation fluid to flow reversely. The kick-back force causes the power cylinder to be operated, with the result that the tires to be steered are undesirably steered against the driver's intention.
Each of Japanese Utility Model Application Laid-Open (kokai) Nos. 1-33419 and 2-533 discloses a technique that solves the above-described problems. In the conventional technique, a check valve is disposed within a pressure port of a control valve in order to prevent reverse flow of the operation fluid.
In the conventional power steering apparatus, however, when a large kick-back force is input from a tire that runs onto a curbstone or the like, the oil pressure within the power cylinder and the control valve increases excessively, resulting in a possibility that the oil pressure within a pump located on the upstream side of the check valve reaches a preset relief pressure. Also, seal parts must have an enhanced seal performance in order to sustain such an increase in the oil pressure.